Blackboard compass



A ril 25, 1961 Filed Aug. 6, 1959 2 Sheets-Sheet 1 77 'f l F757. 2 i l l I J WYM c. T. SCHNELL 2,981,001

BLACKBOARD COMPASS 2 Sheets-Sheet 2 Filed Aug. 6, 1959 BLACKBOARD COMPASS Carl T. Schnell, Herrgardsgatan 65A, Motala, Sweden Filed Aug. 6, 1959, Ser. No. 832,035

1 Claim. (CI. 33-27 This invention relates to blackboard compasses especially of such a type as comprises a pair of similar legs hingedly connected together at their upper end, one of these legs at its lower end carrying a member for centering the compass when 'used on the blackboard and the other of these legs at its lower end carrying a holder for a drawing chalk.

One of the principal features and objects of the present invention is to provide for said type of a compass a chalk holder, which is convenient in use so that it enables a quick shifting of the chalk or a quick adjustingof its length position.

It is a further feature and object of the present invention to provide means for making said chalk holder adjusta ble as to'its angular position in relation to its leg and thus to a proper angular position in relation to the blackboard plane.

Still another object of the present invention is to provide a locking arrangement for said chalk holder, which enables the holder to be locked in the adjusted angular positions.

Still another object of the present invention is to provide forsaid type of a compass a centering member which is advantageous in use in cooperation with the abovementioned chalk holder.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the. appended claim. My invention itself, however, both as to its organization and manner of construction, together with further objects and advantages thereof, may best be understood by references to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a sectional top view of a chalk holder according to the present invention;

Figure 2 is a side view of the same chalk holder; and

Figure 3 is a side view of a centering member according to the present invention.

As shown on the drawing:

Reference numeral 1 designates one of the two wooden legs of the compass, which legs at their upper ends in a manner not shown but known per so are hingedly connected together. The lower part 2 of said leg 1 is turned down to fit into a sleeve 3 formed in a metallic end shoe 4. The lower part of said shoe 4 is provided with a slot 5 made'in the same plane as the two legs of the compass are situated. In this slot 5 there are two holder halves 6 and 7 positioned opposite each other and at their right ends interconnected by means of a hinge 8. The halves 6 and 7 are provided with angularly shaped seats 9 and 10 for a chalk 11. As is seen from Figure 1, the seats 9 and 10 are shaped and dimensioned in such a manner, that when the holder half 7 is pressed towards the holder half 6 by means of a spring 12 the chalk will be clamped from three sides and will be wedged in the holder half 6. Outside of the seats 9 and 10 the two halves are crossed and are at their left ends bent to 2,981,001 Patented'Apr. 25,. 19.61

form finger grips 13 and 14. When these grips against the action of spring 12 are manually pressed towards each other the chalk 11 is loosened and if necessary can I be adjusted in axial direction.

Ascrew 15 is fastened in the metal shoe in such a way that it passes through the slot 5 in transverse direction. About this screw 15 is the holder half 6 rotatablymounted, while the holder half 7 is rotatably mounted about a sleeve 16 coaxial with and screwed on the screw 15. The sleeve 16 passes through the holder half 7 with clearance enough to ensure this half to move about the hinge 8 towards or away from the holder half 6.. The screw 15 and the sleeve 16 function as a pivot for the holder halves 6 and 7, so that these parts can be rotated in the same plane, in which the two legs ofthe compass are situated. The sleeve 16 is provided with a knurled head 17 and is screwed so far on the screw 15, that the end of the sleeve 16 will press theholder half 6 towards the wall of the slot 5 and lock it there. To increase the security of the locking a washer of friction material is arranged about the screw 15 between the wall of the slot and the holder half 6.

When the locking sleeve 16 is loosened the chalkholder 6, 7, with the chalk ll can be turned to a proper p051 tion in relation to the circle to be drawn, after whichq :the locking sleeve 16 is tightenedagain.

When afnew chalk is inserted in the holder aconside'rable length ofit will extend outside the sea-ts 9 and 10 and will there be unprotected against unintentional blows.. To prevent the breakage of this part a cover can be used, this being fastened to one of the holder halves 6 or 7, preferably to the seat 9 of the holder half 6. The'cover. shall extend along the whole or almost the whole length of the chalk above the seats. It can preferably be made of wire of proper rigidity which is wound as a sleeve to surround the chalk and may be wound with intervals between the wire turns to make the chalk visible. It can also be made as a halfround channel, fixed to the seat 9 and supporting the backside of the chalk.

In order to enable the chalk holder here above described to be used in the very best way, the centering. member on the other compass leg has to be so designed, that it allows the angle of inclination of this leg. with the plane of the blackboard to be varied within a widerange without causing the centering member to loosen its grip of the blackboard.

Such a centering member is shown in Figure 3. Here the numeral 18 designates the other compass leg, the lower part-19 of which is turned down'to fit into a sleeve 20, formed in a metallic end shoe 21. The lower part of this shoe 21 is provided with an axial hole 22. In this hole there is inserted a pin 23 pivotally connected to a suction cup 24 of rubber or plastics. For this purpose the pin 23 in its lower end is provided with a ball 25, which is inserted in a cup-shaped ball race (not shown) within the suction cup 24. This device is preferably so manufactured, that the ball race is inserted in the mold when making the suction cup, whereafter the ball 25 is inserted into the ball race and is kept in permanent engagement with said race by for instance pressing the edges of the cup-shaped ball race round the ball. When making this procedure it is necessary to watch that his a clearance between the race and the ball, so the latter will be able to rotate within the race. Thus the device is such that the pin 23 will be rotatable round its own length axis and at the same time will be swingable to various positions of inclination in relation to the bottom plane of the suction cup 24. The pin 23 is locked to the shoe 21 by means of a screw 26 engaging a groove 27 made in the pin 23.

The hole 22 in the shoe 21 is continued upwards by a somewhat larger hole 28 made in the compass leg 18 itself. In the upper part of this hole 28 there is inserted a pressure spring 29, which rests on the head 30 of a centre pin 31, the point 32 of which in turn is resting on the upper end of the pin'23 of the suction cup 24. As is disclosed by the drawing the, centre-pin 31 is guided in aradial direction, at its upper end by its head 30 fitting into the hole 28 and at its lower end by the pin 31 itself fitting into the hole 22.

If it is desirable to use such a centre pin 31 instead of the suction cup 24, this perhaps being the case in school rooms, where old wooden blackboards still are in use, the locking screw 26 is loosened. The spring 29 will then press the pin 23 of the suction cup 24 downwards out of the hole 22 at the same time moving the centre pin; 31 so far downwards, until its headStl is brought into engagement with the bottom of the sleeve, 20, this stopping the further movement of the centre pin 31; A

groove 33 made in the centre pin 31 will now be in front of the locking screw 26, so the pin can be locked to the shoe 21.

'If it is desirable again to use the suction cup 24, the locking screw 26 is loosened and by means of the pin 23 of the suction cup 24 the centre pin 31' is against the action of the spring 29 pressed upwards so far, until the groove 27 of the pin 23 is brought in front of the locking screw 26, after which this is tightened. The various parts will now again be in the positions shown in Figure I claim as my invention: In a holder for a marking element two separate lengthened holder halves arranged opposite each other and hingedly connected together at the one end, seats for said marking element being made in the intermediary part of the halves perpendicular to their length direction, spring means for pressing the one half against the other, thereby clamping said marking element between them, and grips at the other end of said holder halves for manually separating said halves from each other against the spring pressure to loosen said marking element, a transverse pivot being provided near the hinge end of said holder halves for enabling a turning movement of the holder to various rotational positions, locking means arranged coaxially to said pivot and passing freely through the one of said holder halves to engage the other of said halves, said locking means apt to hold said last mentioned half to lock the holder in the rotational position to which it has been brought.

References Cited in the file of this patent UNITED STATES PATENTS 

